1. Field of the Invention
The present invention is related to a driving method of a liquid crystal display (LCD), and more especially, to a LCD of improvement of flicker upon switching frame rate and the driven method for the same.
2. Description of Prior Art
With a rapid development of monitor types, novel and colorful monitors with high resolution, e.g., liquid crystal displays (LCDs), are indispensable components used in various electronic products such as monitors for notebook computers, personal digital assistants (PDAs), digital cameras, and projectors. The demand for the novelty and colorful monitors has increased tremendously.
Referring to FIG. 1, a block diagram of a conventional liquid crystal display (LCD) device 10, the LCD device 10 comprises a pixel matrix 12 having a plurality of pixel units 20, a gate driver 14, and a source driver 16. Each pixel unit 20 comprises a transistor 22, a storage capacitor CS, and a liquid crystal capacitor CLC. The gate driver 14 outputs scanning signals to cause the transistors 22 in each row to be switched on in order. The source driver 16 outputs corresponding data signals to a whole row of pixel units 20 to cause the liquid crystal capacitors CLC to be charged up to respective required voltage. Alignment of liquid crystal molecules between the liquid crystal capacitors CLC is adjusted to exhibit different gray levels according to the voltage level of the data signals. Once the pixel units 20 in the same row finish being charged, the gate driver 14 switches off the scanning signal of the row and then outputs the scanning signal to switch on the transistor 22 in the next row, and sequently, the source driver 16 charges and/or discharges the liquid crystal capacitor CLC of the pixel units 20 in the next row. A sequence like the above continues until all of the pixel units 20 of the pixel matrix 12 finish being charged. Afterwards, the pixel units 20 in the first row start to be recharged. Once the pixel units 20 in each row finish being scanned, the storage capacitor CS stores voltage based on the data signal so that until the next scanning signal arrives, each pixel unit 20 can let the liquid crystal molecules between the liquid crystal capacitor CLC retain the same direction of rotation to exhibit fixed gray levels depending on voltage based on the data signal stored in the storage capacitor CS.
In the current design of the liquid crystal display panels, taking a pixel matrix 12 with a resolution of 1366×768 and a 60 Hz frame rate for example, the display time of each frame is approximately 1/60=16.67 ms. And, the pixel units 20 need to be charged and/or discharged to the required voltage within 14.63 μs to exhibit their corresponding gray levels according to the data signal output by the source driver 16.
In order to reduce power consumption of LCDs, a so-called Seamless Display Refresh Switch Technology (SDRRS) is frequently adopted nowadays. The technology is related that the frame rate is automatically lowered when the frame remains constantly unchanged, for instance, the frame rate being switched from 60 Hz to 40 Hz. Referring to FIG. 2, it shows a timing diagram of a Gate-On-Enable signal OE upon the frame rate being switched from 60 Hz to 40 Hz. When the frame rate is 60 Hz, the liquid crystal capacitor CLC of the pixel unit 20 is charged and/or discharged within Ta (approximately 14.63 μs). When the frame rate is 40 Hz, the liquid crystal capacitor CLC of the pixel unit 20 is charged and/or discharged within Tb (approximately 21.95 μs). The required time TTFT for the liquid crystal capacitor CLC to be charged is approximately 15.3 μs, leading to Ta<TTFT<Tb as the frame rate is switched. That is to say, the liquid crystal capacitor CLC fails to be charged to a required voltage within Ta; and contrarily, the liquid crystal capacitor CLC is able to be charged to the required voltage within Tb. Because of the difference in charge time between Ta and Tb, the difference in brightness that the gray levels exhibited at the instant of the switch of the liquid crystal capacitor CLC causes the frame to flicker.